VBA EXCEL formula in a String

Hi I would like to put into a STRING the following formula

Dim stringAppoggio As String
Dim myMonth As String

myMonth = "January 2020"

stringAppoggio="=DAY(EOMONTH(DATEVALUE(01-'&myMonth&'-&YEAR(myMonth)),0))"

It doesn't really give me a syntax error, but I don't see the result of the formula in the String

Thank you